1. Scope of the Invention
This invention relates to database management systems, and more particularly to graphically querying relational database systems.
2. Description of the Prior Art
All database management systems store and manipulate information. The relational approach to database management, proposed in 1970 by Dr. E. F. Codd at the IBM Research Laboratory in San Jose, Calif. and developed during the following decade by many universities and laboratories, represents all information as "tables." A "database" is a collection of tables. Each table has rows and columns. Each row (horizontal) describes one occurrence of an entity such as a person, a company, a sale or some other thing. Each column (vertical) describes one characteristic of the entity such as a person's name, a company address or a date. Furthermore, each row of a table is uniquely identified by values in one or more of its columns.
All database management systems have some mechanism for getting at the information stored in a database. Such a mechanism involves specifying data retrieval operations, often called "queries," to search the database and then fetch and display the requested information.
There are standard means of formulating queries for relational systems, such as the Structured Query Language (SQL) and Query-by-Example. There are even graphical solutions on the market. However, all of these methods have particular problems associated with them.
Today's standard, SQL, is typed in using English-like syntax. There are particular words or tokens that distinguish particular clauses to do different parts of the query, such as selecting the columns to keep in the result or selecting the rows to keep. One has to know the difficult syntax to be able to formulate the question using SQL. For something like Query-by-Example, there is not much syntax to learn, but the interface is one that must really be explored in depth before queries of any complexity can be developed.
Some companies have attempted to resolve the inadequacies of these methods by coming up with more graphical solutions. They tend to show graphical representations of entities such as tables, and then use connections to link them up and join the information together. They work well for simple queries but cannot be used when the questions get too involved--it is often assumed the more difficult queries can be handled using SQL. However, when SQL is used, queries of greater complexity may be formulated, but then ease of use is lost.
It should be noted that there is a body of related work in the academic literature dealing with graphical database design, semantic data modeling, and even graphical query languages. Typical examples of such work are those described in the following documents:
"A Graphical Data Base Design Aid Using The Entity-Relationship Model," by Chan and Lochovsky, published in the Proceedings, International Conference on Entity-Relationship Approach To System Analysis and Design, 1979, pp. 295-310.
"Graphical query languages for semantic database models" by Czejdo et. al., National computer conference, 1987, pp.617-623.